1. Field of the Invention
The invention relates to a control device and control method for a multi-cylinder internal combustion engine.
2. Description of Related Art
Japanese Patent No. 4089244 describes a control device for a diesel engine. The control device, in an idle operating state, detects a rotation fluctuation of a crankshaft in each cylinder with the use of a crank angle sensor and then updates a correction value, as a learned value, for individually correcting a control value for each fuel injection valve such that the degree of deviation in the rotation fluctuation of the crankshaft among the cylinders reduces (hereinafter, first learning process). By updating the learned value in this way, the degree of deviation in the rotation fluctuation of the crankshaft among the cylinders reduces, so engine vibrations are reduced.
Japanese Patent Application Publication No. 2011-190725 (JP 2011-190725 A) describes a control device for a diesel engine. The diesel engine includes a fuel pressure sensor at each fuel injection valve. Each fuel pressure sensor detects a fuel pressure inside the corresponding fuel injection valve. The control device updates a correction value, as a learned value, for correcting a control value for each fuel injection valve on the basis of the fuel pressure that is detected by the corresponding fuel pressure sensor (hereinafter, second learning process). Specifically, the control device uses the corresponding fuel pressure sensor to detect a manner of fluctuation of the fuel pressure inside each fuel injection valve with the injection of fuel by the corresponding fuel injection valve, and then calculates the correction value for correcting the control value for each fuel injection valve on the basis of the result of comparison between a temporal waveform (detected temporal waveform) of a fuel injection rate that is calculated from the detected value and a basic temporal waveform. By so doing, even when there are variations due to manufacturing or aged deterioration in the fuel injection valves, it is possible to improve the controllability of fuel injection through each fuel injection valve.
Japanese Patent Application Publication No. 2008-144749 (JP 2008-144749 A) describes a configuration that, in an idle operating state, executes both the first learning process and the second learning process.
In this case, as shown in FIG. 5, the first learning process is executed from timing t0 at which the idle operating state is established. By so doing, a correction value for correcting a control value for each fuel injection valve is individually learned as a learned value. At this time, because the second learning process is executed, the correction value for correcting the control value for each fuel injection valve is individually learned on the basis of the result of comparison between a detected temporal waveform, which is calculated from a detected value of the fuel pressure inside the fuel injection valve, and a basic temporal waveform. The first learning process and the second learning process both update the correction value, as the learned value, for correcting the control value for each fuel injection valve, so control interference tends to occur in each process. When control interference has occurred, it may require a lot of time up to timing t3 at which each learned value converges or each learned value may not converge.
In addition, at this time, the first learned value includes various components that contribute to a rotation fluctuation of the crankshaft. However, if both the first learning process and the second learning process are executed, components caused by the fuel injection valves, which should be originally included in the second learned value, are included in the above various components, and it is difficult to eliminate this situation thereafter, so this may impair updating the first learned value and the second learned value with appropriate values.